I'm converting a 1/2 bathroom into a laundry room & needing to replace the 24" door with a 28" door, so standard 27" washer/dryer units can be installed.

There are currently some trim pieces along the drywall sides used to fasten drywall, these can be removed or trimmed down some to gain some space. Doing this will allow the king & jack studs to be moved 4" wider to fit a 28" door.

The Question: can I just replace & widen the bottom 2x4 on the header to the jack studs versus removing & widening the entire header?

If needed, I could also install cripple studs in the 2" spaces now created with widening.

The use of a 28" door will make getting 27" appliances into and out very difficult. The door stops will reduce the opening to no more than 27.5 inches. If at all possible you should fit a wider door.
– Jim StewartNov 29 '16 at 15:08

Jim, it'd be great to be able to install a 30" door, but the two adjoining walls are angled into the door and on the opposite side of this room with 8' ceiling is a room with 12' ceilings........Isherwood, the existing door is only 24" wide, not 2'-4" wide.
– Ken W.Nov 30 '16 at 2:37

Chris, it's a 1988 home, this door is actually on angles to the other two walls. There not stud walls on either side, they're ripped down angled pieces of 2x4's that were used to fasten drywall too.
– Ken W.Nov 29 '16 at 17:57

Concerning the idea of just adding on to the end of the existing header, every framing example I have ever seen has the header as a continuous length of dimensional lumber with its ends resting on the jack studs. I don't know the framing codes but a pieced header must not be according to code.